1. Field of the Invention
The present invention relates to a method of replenishing toner for a housing portion for accommodating therein a dual-component developer composed of toner and carrier, a toner replenishing apparatus, and a computer readable recording medium having a program stored thereon which allows a computer to effect a toner replenishing function.
2. Description of the Related Art
In a development process based on electrophotography, an image is formed by causing toner to be electrostatically adhered to an electrostatic latent image formed on a photoreceptor drum.
FIG. 9 is a view schematically showing a housing portion 1 for accommodating therein a dual-component developer composed of toner and carrier. As the toner is consumed in the course of development process, so the concentration of the toner within the housing portion 1 is caused to vary. In a case where the concentration of the toner within the housing portion 1 is deviated from an intended concentration, it becomes impossible to obtain a desired image due to an undesirable increase or decrease in the density of a developed image, scattering of the toner, and so forth. Accordingly, the concentration of the toner within the housing portion 1 needs to be maintained at the intended concentration by effecting replenishment of toner in an appropriate manner.
Toner is supplied through a toner replenishment inlet 2 formed at one end of the housing portion 1. The housing portion 1 includes an agitating roller for agitating and conveying the toner supplied through the toner replenishment inlet 2. The toner fed into the housing portion 1 is circulated inside the housing portion 1 while being agitated with carrier by the agitating roller. In FIG. 9, a direction in which the toner is moved is indicated by arrows 3. Together with the carrier, the toner is adhered once to a magnet roller 4, and subsequently the toner is adhered to that part of a photoreceptor drum which bears an electrostatic latent image, and it is thereupon consumed. The housing portion 1 is provided with an ATC (Auto Toner Control) sensor 5 for detecting toner concentration. With the necessity of detecting the concentration of the toner in the developer under the condition that the toner and the carrier have been agitated together, the ATC sensor 5 is spaced a predetermined distance away from the toner replenishment inlet 2 on a downstream side in a toner conveying direction. Therefore, according to the related art, there is a time delay of about 5 to 6 seconds before the ATC sensor 5 detects variation in toner concentration resulting from the replenishment of toner through the toner replenishment inlet 2. Furthermore, since the toner is consumed at the magnet roller 4, even if replenishment is required following the consumption of the toner, there is a time delay of about 10 to 15 seconds before the necessity of toner replenishment is detected by the ATC sensor 5.
The larger is the amount of toner consumption in a unit of time, the greater is the variation of the concentration of the toner within the housing portion 1 in a unit of time. When the amount of toner consumption is small, the variation of the toner concentration in a unit of time is insignificant correspondingly. In this case, even if the replenishment of toner is effected to adjust the current toner concentration detected by the ATC sensor 5 to a predetermined concentration, it is possible to keep the toner concentration constant. However, when the amount of toner consumption is large, the variation of the toner concentration in a unit of time is significant correspondingly. In this case, in accompaniment with the replenishment of toner for adjusting the current toner concentration detected by the ATC sensor 5 to the predetermined concentration, the toner concentration is deviated considerably from the intended concentration. Therefore, in a case of effecting the replenishment of toner on the basis of the toner concentration detected by the ATC sensor 5, the toner concentration cannot be maintained at the intended concentration, thus causing a ripple in the concentration of the toner adhered to the magnet roller 4. The time period of the ripple corresponds to the time taken for the toner to go around inside the housing portion 1.
FIG. 10 is a graph showing the variation of the value of output from a magnetic permeability sensor with respect to time and the change of the state of a toner motor between an ON state and an OFF state with respect to time, as observed when toner is fed into the housing portion 1 with use of the related art. In the graph, the value of output from the magnetic permeability sensor is taken along the vertical axis, and the time is taken along the horizontal axis.
The ATC sensor 5 is realized by using the magnetic permeability sensor. The value of output from the magnetic permeability sensor represents the concentration of the toner within the housing portion 1. Moreover, the replenishment of toner is effected during the time the toner motor for rotating a toner bottle is kept in an ON state, but it is not effected during the time the toner motor is kept in an OFF state. According to the related art, the switching between the ON and OFF states of the toner motor is made every time the concentration of toner crosses a threshold value. In this way, the replenishment of toner to the housing portion 1 is controlled. A repeat of the switching between the ON and OFF states of the toner motor results in an increasingly significant variation of toner concentration, and also makes it impossible to achieve continuous toner replenishment.
In a toner replenishing apparatus according to one related art, the amount of toner consumption is calculated on the basis of a coverage rate, the number of pages printed, and a predetermined constant of toner consumption. Then, toner is replenished based on the amount of toner consumption obtained by calculation and the concentration of toner. In this way, the replenishment of toner is effected in accordance with the amount of toner consumption thereby to maintain the concentration of toner constant (refer to Japanese Unexamined Patent Publication JP-A 4-304486 (1992)).
In an image forming apparatus according to another related art, the amount of toner to be replenished is conjectured based on the concentration of toner. Moreover, the amount of toner consumption is measured on the basis of the number of pixels of an electrostatic latent image. Then, a conjectured amount of toner is replenished with each toner consumption. In this way, the replenishment of toner is effected in accordance with the amount of toner consumption thereby to maintain the concentration of toner constant (refer to Japanese Unexamined Patent Publication JP-A 5-88554 (1993)).
In an image forming apparatus according to yet another related art, an output signal from a toner concentration sensor is shifted in accordance with a coverage rate. On the basis of the shifted output signal, the replenishment of toner is effected. In this way, the timing of toner replenishment is changed in accordance with a coverage rate thereby to maintain the concentration of toner constant (refer to Japanese Unexamined Patent Publication JP-A 2002-333774).
In each of the related art constructions thus far described, the replenishment of toner is effected in consideration of the amount of toner consumption. However, in a case of performing printing with a high degree of coverage rate, the amount of toner consumption is large, and the range of variation in the concentration of toner is wide correspondingly. This gives rise to a problem of occurrence of a ripple. Furthermore, the switching between the ON and OFF states of the toner motor is repeated in keeping with the ripple, which results in a further widening of the range of variation in the concentration of toner. This makes it impossible to achieve continuous toner replenishment. As still another problem, a toner shortage may be caused due to a failure of replenishing toner in good time.